Range-change transmissions with a multi-stage main transmission, a splitter group upstream from the main transmission and a range group downstream from the main transmission have long been known and are preferably used in heavy utility vehicles. By means of a usually two-stage splitter group with a gear interval that corresponds to approximately half of an average gear interval between two successive gears of the main transmission, the gear intervals of the main transmission are halved and the total number of gears of the range-change transmission available is doubled. By means of a usually two-stage range group with a gear interval above a total gear interval of the main transmission by approximately an average gear interval between two successive gears of the main transmission, the spread of the transmission as a whole is about doubled and the overall number of available gears of the range-change transmission is again doubled. In combination with a three-stage main transmission (having three forward gears and one reverse gear) this gives a range-change transmission with a total of twelve forward gears and a maximum of four reverse gears, and in combination with a four-stage main transmission (having four forward gears and one reverse gear) a range-change transmission with a total of sixteen forward gears and a maximum of four reverse gears is obtained.
Compared with a single-range transmission with a comparable number of gears and a similar gear gradation and spread, such a range-change transmission has much more compact dimensions and is lighter. However, since many shifts in a range-change transmission entail changing gear steps in more than one part-transmission and therefore take place in a relatively complicated manner, shifts in most known range-change transmissions are designed as partially or fully automated processes.
From the range of automated variable-speed transmissions by the present applicant known as the AS-Tronic family, the transmissions of the AS-Tronic-mid series designed for medium-weight utility vehicles and the transmissions of the AS-Tronic series provided for heavy utility vehicles, being in each case range-change transmissions with a multi-stage main transmission, i.e. one having three or four forward gears, a two-step splitter group connected upstream from the main transmission and a two-stage range group connected downstream from the main transmission, are well known. In each case the main transmission is of countershaft design, provided with unsynchronized claw clutches, and in the case of the AS-Tronic-mid series it comprises a single countershaft and in the case of the AS-Tronic series two countershafts for reasons relating to the optimization of weight and structural space occupation. In both series, the main transmission is optionally available in a direct-gear version (iHG_min=1) or in a fast-gear version (iHG_min<1). The splitter group is in each case designed as an intermediate transmission with two shiftable input constants for the main transmission. In each case the range group is designed as a two-stage planetary transmission with a shiftable direct connection (iGP=1) and, alternatively to that, a shiftable high gear ratio (iGP1).
DE 198 31 293 A1 proposes a modular system with which a number of range-change transmissions designed in that manner with different numbers of gears and various gear ratios can be constructed using structurally similar assemblies and gearsets. In each case the main transmission is of countershaft design and, depending on the version, has two, three or four forward gears and one reverse gear. The splitter group upstream from the main transmission is in each case of two-stage design, also of countershaft configuration, and has two alternatively shiftable input constants of the main transmission. The range group downstream from the main transmission also has two stages; it is of planetary design and has one greatly speed-reducing and one direct gear ratio.
However, for example from EP 0 618 382 B1 it is also known that a splitter group can be of planetary design and a range group can be of countershaft design. The range-change transmission proposed in EP 0 618 382 B1 consists of a multi-stage main transmission of countershaft design and an additional transmission downstream from the main transmission, which comprises a two-stage splitter group and a two-stage range group. In a first version of the additional transmission illustrated in FIG. 2 of the document the splitter group is of countershaft design, whereas in common with the embodiments of the range-change transmission in DE 198 31 293 A1 the range group is of planetary design. In contrast, in a second version of the additional transmission illustrated in FIG. 3 of EP 0 618 382 B1, the splitter group is planetary and the range group is of countershaft design.